DE69219864T2 - Decoupled flow and pressure setting values in an extraction device when using compressible liquids - Google Patents

Description

The present invention relates to a device for the supercritical or near-critical fluid extraction of components from a sample having the features of the first part of claim 1, which are known from EP-A-0 458 125.

In the above-mentioned EP-A-0 458 125, the expansion nozzle device comprises a single expansion nozzle with a variable opening.

From EP-A-0 275 933 the use of several resistance tubes with different diameters as an expansion nozzle device is known.

Supercritical or supercritical fluids can be used as solvents in extraction devices, chromatographs, and other similar devices. The supercritical region is often defined by all temperatures and pressures above the critical temperature and critical pressure. The critical temperature is the temperature above which the difference between gases and liquids disappears; there is a fluid phase for all pressures. No matter how much pressure is applied, the liquid phase cannot be compressed. A supercritical fluid can be defined as a substance at a temperature above its critical temperature, and the critical pressure can be defined as the pressure corresponding to the critical temperature value when plotting the values on a pressure-temperature graph at which liquid and gas coexist for a substance. The lack of possibility of gas-liquid equilibrium is therefore often used to define a supercritical fluid. Supercritical fluids are a useful hybrid of gases and liquids as they are commonly perceived, having a gas-like Viscosity, liquid-like densities, and larger diffusion coefficients than common liquid solvents. The liquid-like density of a supercritical fluid gives it a variable liquid-like solvency over wide density ranges that is essentially a linear function of density. This allows the solvency, usually considered a chemical interaction, to be tuned ("selected") simply by adjusting a physical parameter, namely density or pressure. The variable solvency is most evident at densities corresponding to pressures from about 0.8 times the critical pressure up to pressures at which the density of the solvent becomes almost liquid-like.

Another important aspect of supercritical fluids is that, compared to the usual liquid solvents, the supercritical fluid transport properties in terms of viscosity and diffusion coefficient allow for improved mass transport within complex matrices, such as coal, plant or animal tissues, or packed beds. In other words, the supercritical fluids have better penetration and dissolve almost as well as the usual liquids. Supercritical fluids are therefore more effective for the extraction of complex matrices.

Although the solvency of a supercritical fluid is variable, every supercritical fluid has a maximum solvency that is close to the substance in the liquid state. Although the solvency of a liquid is also variable, essentially as a linear function of density, a substantially greater increase in pressure is necessary to produce a significant increase in the solvency of the liquid. For a common liquid laboratory solvent, such as methanol, the pressure can be reduced to ambient pressure and a solution of the solvent and solutes is stable. To To drive off the solvent, heat must be applied to concentrate or dry the solution. When a liquid with a very high vapor pressure at ambient temperature is used, such as liquid carbon dioxide or ammonia, the solvent can be easily evaporated upon relaxation of the solution, leaving a dry, concentrated solute. However, a discontinuity in density occurs along an isotherm corresponding to the lines between the coexisting liquid and gaseous phases. Because of the discontinuity in density, the solvency essentially becomes large or small, e.g. "it works" or "it doesn't work", and most of the versatility in controlling solvency is lost.

Regarding mass transport properties, the diffusion coefficient is an important parameter. Diffusion coefficients for liquids cover a wide range, some of them (e.g. carbon dioxide and ammonia) are almost equal to those of the supercritical fluid when the liquid is in a near critical state. In these cases, both the liquid and the supercritical fluid would meet the requirements for effective extraction. However, for the liquids commonly used, the diffusion coefficients are a factor of 10 to 100 lower than for supercritical fluids, and therefore these liquids are less efficient in terms of the time required for extraction.

Supercritical solvents are therefore superior in that they (1) allow a large continuous range of solvency, thereby providing selective dissolution of the solutes within this range, (2) provide a means for rapid and complete separation of solvent and solute with minimal heat input, and (3) can reduce the time for extraction of complex matrices by a factor of 10 to 100.

Carbon dioxide is the most important extraction fluid used in supercritical fluid extraction systems because it is inexpensive, harmless, readily available in high purities, and has a critical temperature of about 31ºC, making it suitable for thermally labile compounds. Furthermore, it is soluble in many common solvents. Carbon dioxide has been found to have a similar solvency to hexane. However, there are many applications that require greater solvency, the advantageous properties of supercritical fluids, and moderate operating temperatures for thermally labile compounds. Mixtures of carbon dioxide with modifiers can meet these requirements. As is well known to those skilled in the art, supercritical fluids can be used as solvents in extraction and chromatography; in such applications, carbon dioxide is the preferred solvent. Other fluids that have critical points close to ambient temperature (25ºC), such as ethane, nitrous oxide, ethylene or sulfur hexafluoride, can also serve as the base solvent. The possibility of using these alternatives is not fully exploited due to the inherent harmfulness and greater cost of using these solvents.

Another way to increase the solubility of the solute in supercritical fluid systems is by controlling the temperature. It has been proven that for some solutes a certain minimum temperature is necessary to obtain good solubility of the solute in a supercritical fluid, even at maximum densities, so that via the simple P-T relationship with density, temperature is also a parameter of the solubility.

The problem encountered when constructing extraction systems that extract compressible fluids at pressures above ambient pressure (atmospheric pressure) is that the pressure of the fluid system is coupled to the mass flow rate of the flowing fluid. This is a consequence of the use of constant geometry restrictors to achieve a pressure drop from higher to lower pressures, which normally correspond to ambient or vacuum conditions, but other pressures may also occur, so that the only practical way to achieve higher pressures upstream of the restrictor is to increase the mass flow rate. To maintain the same mass flow rate at higher pressures, an alternative may be to use a fixed geometry restrictor but of smaller dimensions; such a replacement, however, requires some kind of physical intervention. In the operation of these extraction systems, however, it is highly desirable to provide the same mass flow rate at all pressures, i.e. if a lower flow rate is used to obtain the lower pressures, the time required for the flow of a given total amount of fluid may be considerably longer than at higher pressures, e.g. hours as opposed to minutes. For a system that can be set to operate sequentially at different pressures, e.g. 76 bar, 89 bar, 103 bar, 207 bar, 414 bar (1100 psi, 1300 psi, 1500 psi, 3000 psi, 6000 psi) at flow rates that give the same integrated mass of expanded carrier fluid at each pressure, the time to completion of the process may be so long that the process becomes inefficient. This is particularly true when using supercritical fluid extraction systems and near-critical fluid extraction, which may be more efficient in terms of time required than extractions with conventional fluids due to the transport properties (e.g. viscosity and diffusion coefficient) of the critical and near-critical fluids. However, this efficiency is lost if the pressure and flow parameters vary due to the hardware implementation, e.g. due to the constant geometry of the flow restrictors, cannot be decoupled.

It is therefore an object of the present invention to decouple the parameters pressure and flow so that they can be adjusted and controlled independently of each other.

In the past, users of supercritical fluid chromatographs (SFCs) and supercritical fluid extractors (SFEs) have chosen pressure and temperature parameters to indirectly set the desired density parameter. Density is usually a more useful parameter than pressure in supercritical (and near-critical) systems because it has a simple linear relationship to the solvency of the fluid. In all previous implementations of supercritical fluid systems, often only pressure and temperature could be entered; the calculation of the resulting density or even the understanding of the pressure/density/temperature relationship was left to the user, although occasionally assisted by abbreviated look-up tables. In these cases, therefore, control of solvency was dependent on the technical education and persistence of the user, who had to apply the equation of state correctly.

Extraction of solids has traditionally been carried out manually in conventional laboratory glassware containers. Laboratory equipment that automatically performs the soaking of the sample in a boiling liquid solvent together with the subsequent concentration of the resulting solution is sold commercially under the name "Soxtec" (registered trademark) by Tecator. This equipment does not allow fractionation as part of the process; the starting product is not in vessels compatible with automatic sampling equipment and the samples are taken at temperatures boiled, which are determined by the boiling points of the extracting solvents, which can be detrimental to thermally labile compounds. In the recent past, several companies have offered devices that use supercritical fluids: Milton Roy, Suprex, CCS, Lee Scientific/Dionex and Jasco (registered trademarks). The embodiments of these companies are not particularly sophisticated or automated; they require varying degrees of manual intermediate steps. In these embodiments, the full potential of using supercritical fluids for bulk extraction is not achieved.

There has therefore been a long-standing need for a device that could be used to separate different materials from solid samples using supercritical fluid technology. Either the separated materials (extract) or the remaining material (raffinate) can be the component of interest. The separation process is called extraction. Furthermore, there is a need to automate the extraction of solids because these operations usually require a lot of manual labor. When preparing samples for analytical instruments, it would be highly desirable to automate the sample preparation or preparation of the raw samples to obtain a form that is compatible with the common analytical instruments used in laboratories worldwide. The extraction of solids is often accompanied by further treatments such as fractionation (e.g. by column chromatography), concentration, solvent exchange and solution to original concentrations (reconstitution). A process consisting of these basic treatments may actually consist of many (ranging from a few to hundreds) manual steps. It would therefore be desirable to produce a device that replaces the above-mentioned basic treatments, so that the only step required is to place a sample in the extraction device and to accept fractions of the isolated material in containers that are compatible with the automatic sampling devices of the analyzers.

Improvements in the separation of a selected material from the solid samples and the automation of the typical processing steps of the processes, such as extraction, fractionation, concentration, solvent exchange and reconstitution, are clearly desirable goals. It would be desirable and of significant benefit to have a method that differs from the conventional laboratory processing steps known to the person of ordinary skill in the art if such a new technique would provide superior properties in any of the following areas: quantitative determination, repeatability and reproducibility, speed, automation, automatability, reduction of health risks or reduction of costs (for materials and laboratory).

Ideally, an extraction device would be a stand-alone module, i.e. a single device within an integrated system. In such a system, it is also highly desirable to provide robotic access for sample loading and fraction retrieval in an automated operation. An important aspect of any extraction system is therefore the upgradability for automation of sample input (i.e. adding an automatic sampler for solid samples) and automation of fraction output (i.e. collecting fractions through further chemical treatment and queuing on a large scale); an external pump module for mixing the extraction fluid composition could be another future addition.

A further improvement for the usability of the extraction systems would be the use of standardized input and output containers for the sample that is input and the fraction solutions that are output. The device would therefore be equipped with a multi-size extraction chamber that accepts the solid samples.

An improved extraction device would also include an automated "process," where the process is defined as a sequence of processing steps, each associated with a sample. Examples include, but are not limited to, actuation of valves, changing setpoints (or target values) of heat zones, selection of extraction fluid solvent, selection of reconstitution solvent, selection of flow path, destination of output fraction, changing density/pressure setpoints (target values), changing flow rate setpoints (target values). Such an automated extraction device would further provide automatically selectable destinations for output within a process and from process to process; and automatically selectable within a process and from process to process composition of the input fluid; and within-process and from process to process automatically selectable rinse solvents for the solvent exchange/reconstitution emulation processes.

The object of the present invention is to replace the known single variable nozzle with an arrangement which can achieve discrete pressure levels.

This object is solved by claim 1. Preferred embodiments of the invention are claimed in the subclaims.

The present invention is also suitable in certain embodiments for providing methods and devices in which the device, in particular the nozzle device, can be rinsed with a solvent in order to prevent blockage or to avoid other difficulties associated with the accumulation of solids. Furthermore, certain embodiments of the invention may include additional means for selectively diluting the extraction fluid stream after it has energized the extraction chamber.

Figure 1 is a simplified schematic representation of an extraction system according to the present invention;

Figure 2 shows another simplified representation of a further embodiment of the present invention;

Figure 2A shows an alternative embodiment of the system shown in Figure 2;

Figure 2B is a schematic representation of one implementation of a variable fixed throttle that can be used in the present invention;

Figures 2C and 2D show other embodiments of the variable fixed choke shown in Figure 2B ;

Figure 3 shows a schematic representation of an embodiment of an extraction device according to the present invention;

Figure 4 is a schematic diagram, similar to Figure 3, showing an embodiment of the present invention having a flushing section capable of minimizing inclusions;

Figure 5 is a preferred embodiment of the flushing section shown in Figure 4 for minimizing inclusions;

Figure 6 shows a further embodiment of the present invention according to Figures 4 and 5, which includes a flushing section to minimize inclusions, as well as a valve through which flushing takes place;

Figure 7 is another embodiment of the apparatus with a flushing section for minimizing inclusions, using a single pump for both the extraction fluid and the flushing fluid;

Figures 7A and 7B show schematically the location of the connections in a valve used in the embodiment of Figure 7;

Figure 8 shows an embodiment of the present invention with a device for diluting the extraction fluid;

Figure 9 is another embodiment of the device shown in Figure 8; and

Figure 10 shows a further embodiment of the device of Figure 3 with further improvements.

It should be understood that the embodiments shown correspond to the claims, the nozzle device being constructed according to the claims and as described with reference to Figure 2B.

According to a first aspect of the present invention, the set points (or set points) for flow and pressure are decoupled. A user can start a supercritical fluid extraction process according to the present invention by placing the sample in the flow system and entering set points for temperature and a set point for pressure or a set point for density. If the latter is selected, the set point pressure must be calculated using the entered set point for density. The operator then enters a set point flow rate, the length of time for the static and dynamic extraction steps - which determine how long the sample remains or "soaks" in the stagnant extraction fluid and how long the extraction fluid then flows through the sample - along with the system parameters. The method of the present invention then repeats the selection of parameter set points for all steps to produce a complete extraction cycle that changes these parameters in the order prescribed by the user. Upon issuing a "start" command, the instrument executes then performs the following steps: (1) withdrawing the fluid, either as a gas layer or as a liquid layer, from conventional gas cylinders containing contents at pressures above ambient or atmospheric pressure; (2) directing the withdrawn fluid to a pump that is electronically controlled to deliver the fluid to the rest of the extraction system at the selected flow rate; (3) sensing the system pressure while injecting the fluid system; (4) controlling the size of a nozzle orifice to achieve the target pressure during injection of the fluid into a closed system; (5) beginning a timing measurement for comparison to the target extraction times; (6) controlling the nozzle orifice to an appropriate degree of restriction and thereby maintaining a target pressure and temperature with no flow through the sample for the equilibrium time specified by the user. After this is completed, fluid injection into the system is continued at the target flow rate, also referred to as dynamic extraction. The fluid is then directed through a flow path that passes through the sample container section. The system then directs the fluid mixture exiting the sample container section to the expansion nozzle section and maintains all controlled set points for flow, pressure and temperatures until the entered dynamic extraction time has elapsed.

Referring now to Figure 1, there is shown an embodiment of the extraction system of the present invention using the supercritical or near-critical fluids. The system first pressurizes carbon dioxide or other fluids or fluid mixtures from a gas cylinder 100 by means of a pump 102 having a regulator 104 which regulates the desired pressure. The flow system directs the pressurized fluid to an extraction section 106 containing a sample having components which are to be separated. The system then directs the fluid solution to a nozzle 108, where it is expanded to lower (e.g., atmospheric) pressures. In the embodiment shown, the nozzle 108 has a variable orifice which is adjusted to create a restriction which limits the mass flow velocity or flow rate. In a particularly preferred embodiment, the variable orifice is created by means of an axial drive valve such as that disclosed in US-A-5,009,778. In this embodiment, steps (4) and (6) discussed immediately above would provide active control of the orifice. Alternatively, as indicated above, a series of fixed orifices may be provided and interchanged to provide discrete pressure levels, e.g., 76 bar, 89 bar, 103 bar, 207 bar, 414 bar (1100 psi, 1300 psi, 1500 psi, 3000 psi, 6000 psi) at flow rates which give the same integrated mass of expanded carrier fluid at each pressure setting. Such a system is generally useful in an extraction device, and such "step-by-step" variable "orifices" are nonetheless useful in certain embodiments of the present invention. In such a system, various valves must be operated to obtain the static extraction conditions. Alternatively, in a system according to Figure 1 with a manually adjustable orifice restriction, the user must sense the flow rate and adjust the orifice.

In the embodiment shown in Figure 1, the target pressure is preferably obtained by controlling the speed of the pump 102 using the controller 104. The controller 104 is part of a feedback loop from a pressure transducer 112 which provides a signal to the pump mode speed controller 104 to obtain stable operation at the selected target pressure. A flow transducer 118 is provided as part of a control loop 116 which controls the physical constriction of the variable orifice of the nozzle to control the target flow rate in those embodiments which use an electronically variable orifice restriction. The two decoupled parameters are therefore set independently of each other.

In another preferred embodiment of the present invention, shown in Figure 2, the fluid is pumped by a metering pump 102 at a given flow rate set by metering control electronics 204 to provide the remainder of the flow system with a controlled mass flow rate. Again, the fluid flows through the sample in an extraction section 106 submerged in the flow path, dissolves material from the sample, and experiences a pressure drop at nozzle 108. Nozzle 108 serves as a restrictor causing the pressure drop in the high pressure solution to recover dissolved material precipitating from the expanding extraction fluid, and as a vacuum regulator for the pressure system. In these variable orifice embodiments, a control loop 110, using a signal from a pressure transducer 112, controls the physical restriction of the nozzle 108 to maintain a set pressure at all possible values of mass flow rate rated by the pumping system in the range of no flow to about 4 g/min. As discussed above, and as will be understood by those of ordinary skill in the art, a variable orifice nozzle 108 can be implemented in a variety of ways; for example, a modified needle valve can be constructed with particular attention paid to the design of the relief region, or the valve can be constructed in accordance with the above-identified valve disclosed in US-A-5,009,778. Alternatively, in a system such as that shown in Figure 2 with a manually variable orifice restriction, the user must be able to sense the pressure and adjust the orifice.

A modification of the system shown in Figure 2 is shown in Figure 2A. In this embodiment, a flow transducer 126 is added downstream of the pump 102. The flow transducer 126 provides a flow feedback signal to the pump controller 103 and allows the system to monitor the flow rate on the high pressure side of the pump. Although the flow transducer 126 is shown at a position upstream of the extraction section 106, it could also be located downstream of the extraction section 106. The flow transducer 118 can be placed even further downstream of the nozzle in a configuration like that shown in Figure 1, but with a flow rate control loop for controlling the pump.

The embodiments of the present invention disclosed herein with variable nozzle orifices for systems according to Figures 1, 2 and 2A would ideally provide an approximate continuum of target pressures and target flows. As indicated above, the alternative of providing and interchanging a series of fixed orifices provides only a certain number of discrete pressure levels at similar flow rates. Also, the precision and accuracy of control of the flow and pressure parameters is much more difficult to achieve with fixed orifices. Tolerances in the manufacture of such fixed orifice restrictors must be very closely maintained - especially those contributing to the cross-sectional areas because they are squared. When operating such a fixed orifice system, any blockage of the flow passage within the orifice - by clumps of the expanding mobile phase, by precipitation of clumps of already dissolved solutes, or by insoluble particles generated by abrasion of the equipment or from the extracted samples - will alter the mass flow through the orifice, causing a deviation from the setpoints for pressure and/or flow rate. Electronic control of the relative spacing of the variable orifice orifice orifice allows real-time modification of the orifice via the control loop, so that the setpoints are maintained throughout the entire operation of the system can be maintained more stably for many conditions and sample types. In embodiments that use fixed orifices or manually adjustable orifices, manual intervention is required periodically to achieve and maintain the setpoints while the system is operating.

In Figure 2B there is shown an embodiment of a variable restrictor 108, discussed above with reference to Figures 1, 2 and 2A, comprising a plurality of fixed restrictors 114 connected between and connecting two multi-channel valves 115, 116, which valves selectively connect the pressurized fluid flow to one of the fixed restrictors 114. The arrangement of fixed restrictors 114 includes restrictors with different orifice sizes so that a certain mass flow rate and/or pressure can be achieved. As mentioned above, depending on the device in which this variable restrictor 108 is installed, a stepwise independent selection of pressure and flow can be achieved by changing the degree of restriction. As will be understood by one of ordinary skill in the art, the fixed restrictors 114 comprise pinhole fittings, capillary tubes, frits or other such structures having a suitable restriction or throttling that can be connected to the device to be controlled. By using an appropriate combination of hydraulic lines, valves 115, 116 and restrictors 114 and implementing the proper logic algorithms in the control system, the selection of the independent pressure and flow set points can be automated without manual intervention by the user.

As shown in Figure 2C, another possible embodiment of a variable throttle 108 that includes multiple fixed throttles 114 with different degrees of throttle may be constructed in a single flow path. Unlike the embodiments of Figure 2B, the embodiment of Figure 2C requires manual intervention and interruption of the pressurized fluid flow to change the degree of restriction. The fixed restrictor 114 is simply selected from a group of fixed restrictors 114 designed to be interchangeable and inserted into the pressurized fluid flow as shown. This embodiment of the variable restrictor 108 is therefore similar to the case of providing a manually adjustable needle valve; however, if a needle valve is used, the multiple discrete fixed restrictors 114 would be unnecessary. Such an embodiment requires a fundamentally different sequence of process steps because the flow must be interrupted each time the degree of restriction is changed.

It should be noted that in both the embodiments in Figure 2B and Figure 2C, the flow rates at several of the restrictors 114 may be the same so that only the pressure referred to as the set pressure changes. Conversely, the setting values for the flow rate may be different and the setting values for the control pressure may be the same for the different restrictors 114. Providing a step-by-step selection of the restrictor components allows the user to select the combinations of flow and pressure largely independently, thereby achieving a certain decoupling of these parameters.

Finally, another embodiment of a variable throttle is shown in Figure 2D. In this embodiment, the fixed throttles 114 are manually changed as explained above with reference to Figure 2C. However, by providing two-channel valves 117, 118 and two flows, the flow of the pressure fluid does not have to be interrupted each time a throttle 114 is changed. As with the embodiment of Figure 2B, this embodiment allows for step-by-step, independent on-line selection of the pressure and flow setting values. The provision of two flow paths and suitable valves 117, 118 allows the throttles to be set during operation of the device, ie without interrupting the flow.

When supercritical fluids are used, the density parameter, which is a function of pressure and temperature, is directly related to the solvency of the fluid; the solvency is therefore adjustable and selectable by adjusting and controlling two of the three parameters. Since pressure transducers are common, while density transducers are not at the operating conditions of common extraction equipment, it is preferable (but not absolutely necessary) to select the desired operating density and temperature, calculate the correct operating pressure, and control this pressure value. Independent control of pressure and flow allows the chemist to vary the solvency of the extraction fluid by selecting the operating pressure and to vary the rate (or efficiency) of the extraction fluid throughput by varying the flow rate of the pump. With the decoupled parameters, the user can extract over the entire range of parameters during a selectable period of time, i.e., the total amount of extraction fluid. Essentially, all of the following parameters are now independent: flow rate, pressure, and time. In certain embodiments of the present invention, the temperatures of many sections of the flow system are also independently controlled as a fourth parameter.

As will be readily understood by those of ordinary skill in the art, the present invention provides a significant advance in the development of supercritical chromatography (SFC) by maximizing chromatography or adsorption efficiency. The common prior embodiments of SFC extraction devices used fixed restrictions (holes, specific lengths of capillary tubing, frits, etc.) to provide the necessary pressure drop when operating with the supercritical and near-critical carrier fluids (also known as mobile phases These fixed restrictors typically had diameters in the micrometer range. Such fixed restrictors found in the prior art differ from the "step-by-step" variable restrictors and from the actively controlled variable restrictors described here, which can be used to control flow in accordance with the present invention. In the application of SFC, the utilization of the parameters density (pressure), flow rate and temperature is as important as in supercritical fluid extraction (SFE). With the fixed restrictors, in order to perform chromatography, one must adjust the operating pressures by changing the flow rate. This is disadvantageous, however, because in chromatographic separation, the flow rate is an important parameter for separation efficiency. Often the flow rates necessary to achieve high pressures are much too high to reach the most effective chromatography region, i.e. the minimum of the van Deemter curve. The independent control of pressure (density) and flow rate in accordance with the present invention therefore enables good chromatography operation.

In Figure 3, a preferred embodiment of the apparatus according to the present invention for the extraction of components from solids, semi-solids and small volume liquids is shown. The apparatus comprises several inlet channels for extraction fluid, each of which has a valve assembly 101, in some cases accompanied by a downstream check valve 203, to allow a channel selection from several to one as required. Furthermore, a heat exchanger 204 for controlling the fluid temperature upstream and immediately before injection into the pump 202 can be provided. The solvent then flows through a high pressure pump 202, which can be thermally controlled to obtain the desired fluid compressibility in the pump chambers. In order to dampen the pressure fluctuations when pumping the fluid, downstream of the pumps 202 a pulsation dampener 205 is provided. The flow is then divided into two sections, referred to as the "bypass" and "chamber" sections. Valve means 207, 209 are provided for directing the flow to one, both or neither of the said sections.

The chamber portion of the flow system is controlled by the lower valve 209 shown in Figure 3. A preheater 211 may again be provided in this portion of the flow system to control the temperature of the solvent. An additional preheater 240 may also be provided in the bypass portion. The fluid then flows into the chamber 210 where extraction takes place. As shown schematically, the chamber 210 of the present invention is preferably actuated between two positions. This actuation allows for the automated use of the chamber 210 and the automated establishment of the high pressure seals required between the chamber 210 and the vessel containing the sample. As the chamber 210 is moved between the two positions shown, flexible connections are provided, including tubing for the fluid connections and flexible electronic connections for thermal, control and power signals, because the apparatus of the present invention must be able to direct the fluid to the section being controlled.

The sample input module contained in the chamber 210 preferably allows a sample to be introduced into the fluid stream via the extraction chamber 210, with all required seals subsequently being created by activation. The design of the connection point of the sample input vessel and the actuating devices preferably allows cylindrical containers of different sizes to be accommodated. The sample input module, referred to as a "thimble", is preferably a common vessel in an automated laboratory bench, so that the same vessel can be used as a sample transport vessel, as part of a solid phase extraction cartridge and as part of a filter device and for other functions.

As indicated above, in certain embodiments, the flow system of the present invention may include a bypass section controlled by the upper valve 207 shown in Figure 3. The bypass section directs the fluid flow around the extraction chamber section 210 containing the sample to achieve equilibration of all regulated set points before sampling the contents of the solution from the chamber/cylindrical container. The pressure of the fluid delivered by the high pressure pump is measured by a pressure transducer 201 shown located in the bypass section. However, in other embodiments of the present invention, the transducer 201 may be located elsewhere, or one or more additional transducers may be provided to more fully monitor the pressure of the various pumps in the flow system.

A reasonable adjustment of the solvency of the extraction fluid relative to the pressure/density is achieved by means of the pressure transducer 201. As one of ordinary skill in the art will understand, such a pressure transducer 201 must meet reasonable accuracy and precision specifications. The transducer 201 is preferably a mechanical component with a minimum dead volume for fluid flow and is located close to a vacuum control subassembly and relatively close to the exit of chamber 210 to minimize the pressure drop for these two sections. One of ordinary skill in the art will also readily understand that Figure 3 is only a schematic representation of the present invention and that the relative arrangement of the components described will depend on the operating specifications of the system and the performance of the components selected.

The above-described flow paths through the bypass and the extraction chamber are then rejoined at a junction point 213 and lead into the nozzle/separator unit 214 using suitable valve means and filters. To minimize interference with the nozzle/separator unit 214 due to solid particles, a filter 215 is preferably provided immediately upstream of the nozzle/separator unit 214. In certain embodiments of the present invention, the nozzle/separator unit 214 may be manufactured in accordance with the above-referenced US-A-5,009,778.

The flow is then directed to the subassemblies that form the sample acquisition section of the system by subjecting the high pressure fluid to a pressure drop in the nozzle assembly 216, where the pressure fluid is pure extraction solvent, mixed extraction solvent, and/or mixtures of extracted components dissolved in the extraction solvent. The pressure drop allows for separation of the extraction solvent from the dissolved components because high vapor pressure liquids such as liquid carbon dioxide or subcritical or near critical mixtures of fluids such as carbon dioxide and methanol expand when a pressure drop occurs.

The nozzle unit 216 also has a vacuum control function as part of the pressure control loop as well as a thermal control range. However, the flow control is independent of the pressure/density control or regulation. As explained above, in a preferred embodiment of the present invention, flow control is provided by means of a pump 202; however, in other embodiments, as also described with reference to Figures 1 and 2, it is possible to use the nozzle 216 for flow control and control the pressure and density with the pump 202.

For those fluids that remain liquid when they experience the pressure drop at nozzle 216, separator unit 218 is used to vaporize them downstream. Separator unit 218 has a section for diverting the expanding gas stream carrying precipitating extracted components. Separator unit 218 can be filled with a porous or granular material that is either inert or chemically active, such as adsorbents, or has a chemical function, such as stationary or combined liquid phases. One of ordinary skill in the art will readily understand that the packing used in separator unit 218 is a parameter that the user can exploit for fractionation.

Fractionation downstream of the extraction chamber 210 in a supercritical fluid extractor constructed in accordance with the present invention can exploit the richness of the stationary phases and has been shown to achieve the same specificity as in the various areas of analytical and preparative chromatography (e.g., gas-liquid and gas-solid chromatography, normal and reversed phase liquid chromatography, normal and reversed phase thin layer chromatography, adsorption chromatography, supercritical fluid chromatography, size exclusion chromatography). Thus, in certain embodiments, the device described herein can produce chromatography-like selectivity for clean-up of samples in the analytical laboratory due to the interaction of the stationary phase on the fractionation capability inherent in a supercritical fluid extraction device.

There are several ways to obtain the "hyphenated" solution described above. The first is to relax the solution and deposit dissolved components on the separator 218, which is part of the variable nozzle/separator assembly 214. This deposition should occur in as narrow a zone as is practical. A mobile phase is then passed through the separator 216 to move the components through the stationary phase material of the separator with a selectivity as explained above. This can be achieved, for example, with a liquid so that the uptake simulates liquid chromatography. Other embodiments can use temperature and a gaseous mobile phase so that the migration is more similar to gas chromatography, or in the extreme case, thermal desorption. Preferably, a near critical or supercritical fluid is used as the mobile phase. In the last example, this would allow the introduction of a fraction into a supercritical fluid chromatograph, for example by attaching connections to the nozzle/separator unit 214 so that the separator 218 is part of a chromatographic sampling system.

Another embodiment, shown in Figure 10, would include a fractionation zone 300 interposed between the sample chamber 210 and the expansion nozzle 216. In this case, selectively retaining a portion of the components dissolved in the extraction fluid in the fractionation zone 300 as it exits the sample chamber 210 would alter the group of extractants deposited in the collection region, i.e., in the nozzle/separator unit 214, upon expansion. Suitable valving 302, 304 together with temperature and pressure control allows the subsequent removal, possibly in selective steps, of the retained components from the fractionation zone 300 - again with accumulation in the nozzle/separator unit 214. Yet another embodiment could provide for a stationary phase to be introduced into the sample chamber 210 with the sample so that the additional selectivity is superimposed.

Separations of groups with similar functionality, physical structure or molecular weight are important applications for the "hyphenated" fractionation embodiment of the present invention just described. Often, fractions obtained with extractants require further processing and it is often the goal of an analytical chemist to generate groups from compounds with similar structures (e.g., monogalactosyl diglycerides separated from digalactosyl diglycerides, branched hydrocarbons separated from straight hydrocarbon chains, saturated hydrocarbons from unsaturated hydrocarbons, high molecular weight polymers from oligomers and solvents). Various prior art chromatographic studies demonstrate this need. An early industry study of supercritical fluid separations on stationary phases demonstrated separation based on shape/size: a mixture of n-paraffins and isoparaffins was separated into two groups using a molecular sieve packing, which is discussed in W. Ecknig and HJ Polster, Supercritical Chromatography of Paraffin on Molecular Sieve, Part I. Methodological Fundamentals and Part II. Chromatographic Behavior Depending on Mobile Phase Pressure, Chemische Technik (Leipzig), 31 (1979), pp. 89 and 245. Another example is the replacement of the industry standard fluorescence indicator adsorption (FIA) analysis, which is presented in Norris and Rawden, Anal. Chem. 56 (1984), page 1767, in which all saturants, olefins and toxicants are separated from a petroleum product using stationary phases of silica and silver nitrate impregnated silica and a supercritical fluid mobile phase. Finally, several examples of "Dense Gas Exclusion Chromatography" have been disclosed, studying several mixtures and porous silica glass stationary phases. See "Dense Gas Chromatographic Studies", L. Bowman, Ph.D. Dissertation, University of Utah, 1976, Chapter IV. It should be noted that the term "dense gas" is a term previously used to describe supercritical fluids.

Thus, as seen in Figure 10, either a gas chromatograph 500 or a liquid chromatograph 510 can be connected via a high pressure valve 502 at a point downstream of the extraction chamber 210 and upstream of the nozzle/separator unit 214. Both the gas chromatograph 500 and the liquid chromatograph 510 preferably have a nozzle/separator unit 214 as a part of the respective chromatograph 500, 510.

In certain embodiments of the present invention, the separator 218 also has an independently controllable temperature zone that can be operated between a sub-ambient and heated condition. For extraction fluids that do not vaporize upon pressure drop, the temperature control of the separator unit 218 is used to vaporize such fluids as hexane or modifiers used to prepare modifier-carbon dioxide mixtures. After collecting the extracted components, the temperature of the separator can be further increased to a level sufficient to thermally desorb the collected components that would be transported by a gas-like mobile phase with an appropriate setting of pressure and flow rate, identical to analytical instruments such as gas chromatographs, supercritical fluid chromatographs, and liquid chromatographs.

The apparatus of the present invention according to Figure 3 preferably comprises one or more controllable branch valves 220 having different positions that allow vapors to be directed to outlet/waste positions during extraction and rinse solutions to be directed to collection devices of different sizes or to outlet/waste channels during the rinse steps. The controllable diverter valves 220 preferably perform their valve function with a minimum dead volume. Further, valving means are provided to direct the purge fluid streams or exhausted extraction fluids to various destination locations. For example, a first destination is a dividing column 222 terminating in a liquid effluent 223 and a gas vent 224. A second destination is a remote port 225. The dividing column 222 operates at low temperatures and uses demister devices to separate liquid modifier from the vaporized base extraction fluid or to collect liquid solvents.

As also seen in Figure 3, a flow converter 226 or rotameter is preferably mounted on top of the dividing column 222. The dividing column 222 is also connected to the controllable diverter valve 220 which has channels through which the rinse solvents are supplied. A valve 227 (or several valves) is provided to select one or more rinse solvent streams from one or more rinse solvent reservoirs 228 which feed the rinse solvent pump 230 which can withstand the system pressure. The rinse solvent pump 230 preferably has a variable output rate suitable for liquid chromatography range movement and can be adjusted to deliver user selectable volumes to the desired destination. The flush solvent pump 230 can be equipped with an active inlet valve 231 or an active outlet valve 232 for more reliable operation. These valves can also be conventional check valves or switching valves.

Thus, under selected conditions, the rinse solvent is directed through the rinse solvent pump 230 and the diverter valve 220 into the separator unit 218 to dissolve selected components and move them to the user-selected destination for fraction collection. The rinse solvent can move the separator 218 relative to the flow of the extraction fluid during the extraction step in a forward or reverse flushing mode. Figure 3 shows a backflushing system, although forward flushing also forms a preferred embodiment of the present invention. The present invention therefore enables the removal of deposited components by either backflushing or by forward flushing with a second fluid, e.g. with common liquids such as organic solvent systems, acids, bases, aqueous solvent systems; subcritical, near-critical and supercritical fluids, including mixtures, or by thermal deposition in a gas stream. As will be explained in more detail below, other embodiments of the present invention enable these flushing steps to involve one or more sections of the device in addition to the nozzle/separator unit 214.

The separator unit 218 is connected to a liquid drain channel 223, a remote port 225, and automatic liquid sample vials 236, preferably in a queue, via a control valve 234, which may be similar to the diverter valve 220 described above. The control valve 234 supplies a sample vial 236, which is preferably moved up and down to facilitate automation, as described above with respect to the extraction chamber 210. Thus, in a preferred embodiment, the present invention also includes a queue of sample vials 236 that can accommodate multiple fractions in sample vials, such as the automatic sample vials commonly used in gas and liquid chromatographs. There are numerous variations in how a supercritical fluid extraction device made in accordance with the present invention can be operated to obtain optimal recovery while minimizing downtime during maintenance or servicing.

As explained above with reference to Figure 3, in certain embodiments of the present invention, the flow is divided into two sections referred to as the "bypass" and "chamber" sections. To this end, valves 207, 209 and other flow control devices are provided to direct the flow to either, both, or neither of the two sections (bypass and chamber), respectively. The bypass section bypasses the fluid flow through the extraction chamber 210 containing a sample in the sample input module to allow all regulated and controlled setpoints to equalize with the flow before sampling of the contents of the solution in the extraction chamber 210 is initiated. The flow paths of the bypass and chamber sections are preferably joined at a junction point 213 and then flow into the nozzle/separator unit 214 using suitable valves and filters. The present invention also provides further flow control means to separate the majority of the high pressure flow path from the low pressure purge section. Preferably, a filter device 215 is provided upstream of the nozzle/separator unit 214 to minimize interference with the nozzle subassembly 216 by an accumulation of solid particles. As shown in Figures 4 and 5, such valves 251 may also be used in these embodiments to direct the flow through a filter 215 and separate the majority of the high pressure flow path from the low pressure purge section.

In certain embodiments of the present invention, the valves 207, 209 and 212 and the pressure isolation valve means 251 mentioned above (which serves to isolate the high pressure flow path from the low pressure purge section) allow the apparatus according to the present invention to be designed and operated in such a way that the problems frequently encountered in supercritical fluid extraction are avoided. These problems include clogging one or more of the fluid control components of the extraction device between the section containing the samples and the area immediately downstream of the restrictors used to maintain system pressure by providing a pressure drop, e.g., with a nozzle 216. The blockage occurs as a result of precipitation of dissolved components in the flow, extrusion of molten matrices or matrix components into the flow, solid particles of the sample that are too small to be captured by the filter devices 215, or erosion of particles from the device itself, such as metal fillings and polymer particles from sealing components, and subsequent accumulation of these solid particles.

In the purging processes of the present invention, the fluid is supplied either at a pressure and flow rate suitable to release insoluble solid particles and transport them through the throat section (or throat) to the downstream expansion region, or at a pressure, flow rate and solvency suitable to dissolve or dissolve precipitated, precipitated or adsorbed components and transport the resulting solution through the throat section of the nozzle 216 to an expansion region such as the separator 218. Finally, the purging process ends with the restoration of the system configuration so that the purge solvent supply is disconnected from the high pressure side of the nozzle 216.

A preferred embodiment of the present invention thus provides a device that allows the nozzle throat to be flushed to prevent the accumulation of solid particles. First, the supply 228 for the flushing solvent is connected to the inlet line to the nozzle 216. This connection takes place on the high pressure side of the device during pressure generation. The connection is preferably accomplished by activating a valve 251 as shown in Figures 4 and 5 and may occur immediately upstream of the nozzle inlet or alternatively at any other point in the device which ultimately allows flow of solvent to the inlet of the nozzle. The connection may thus be made at a valve upstream of the pump 202 and heat exchanger 204. Certain embodiments of the present invention may also have a device for varying the size of the throat portion of the nozzle 210. The best way to accomplish this would be a nozzle 216 with a variable annular nozzle orifice, most preferably having electronic control of the orifice size as discussed above.

In Figure 4, another preferred embodiment of a supercritical fluid extractor according to the present invention is shown which includes a device for flushing the neck portion of the nozzle 216. As shown, a valve 251 which separates the flush solvent reservoir 228 from the nozzle 216 is located immediately upstream of the nozzle 216 and allows for control of the flow and flushing of the nozzle 216 as needed.

Alternatively, the means for flushing the throat portion of the nozzle 216 may be constructed as shown in Figure 5. In this embodiment, the valve 251 which separates the flush solvent reservoir 228 from the nozzle 216 is upstream of the filter means 215 described above, which in turn is upstream of the nozzle 216. The advantage of this embodiment is that any soluble material deposited on the filter means 215 and the valve 251 is removed from other components such as valve lines, fittings, the inner surface of the tubes, the pre-expansion area of the nozzle 216 and other parts of the nozzle/separator assembly 214 by the flushing process. Another advantage is that the filter 215 protects the nozzle 216 against particulate matter. which may be present in the flush solvent, as well as abrasive particles which are commonly found in control valves. The embodiment shown in Figure 5 thus cleans the nozzle 216 and keeps it free of both solid particles and deposited soluble material. The device shown essentially provides for ongoing maintenance which the user can understand. This embodiment of the device minimizes equipment failures and the need for user intervention to correct faults which are commonly caused by clogging in existing extraction systems.

Figure 6 shows another embodiment of the apparatus according to the present invention suitable for flushing the throat portion of the nozzle 216. In this embodiment, the valve 251 separating the flush solvent reservoir 228 from the nozzle 216 is slightly different than in Figures 4 and 5. The valve 251 is located at some point upstream of a filter device 215 which is upstream of the nozzle 216 and in a flow path which does not pass through the sample. In this embodiment, the apparatus uses the valve 212 which is located near the junction 213 of the flow paths of the bypass and chamber portions to control flow, particularly to prevent or allow flow of liquid solvent into the chamber 210. In the embodiment shown in Figure 6, the valve 251 preferably has at least three channels, labeled A, B, C. As shown, channel "C" is connected to the flush solvent pump 230. Channels "A" and "B" ensure continuous flow during extraction by isolating the flush solvent pump 230 from the system. However, during the flush steps, channels "A" and "B" of valve 251 are connected to one or more other "A" and "B" channels, as seen in Figure 6. For example, channels "A2" and "B2" are located downstream of the bypass pressure transducer 201. Channels "A3" and "B3" are downstream the bypass preheater 240; channels "A4" and "B4" are located immediately downstream of the pulsation dampener 205; and channels "A5" and "B5" are located immediately downstream of the extraction fluid inlet check valves 203. To better illustrate the present invention, the connections between channel pairs "A" and "B" are not shown. These or other connection points may be made, as will be understood by those of ordinary skill in the art, to provide various points where the solvent from the solvent reservoir 228 may be introduced to flush the device. In addition to the advantages discussed above with respect to the device of Figure 5, the embodiment shown in Figure 6 has the further advantage of allowing for more thorough cleaning, that is, a larger portion of the device is flushed during each flush cycle.

Figure 7 shows another embodiment of the device according to the present invention with which the throat portion of the nozzle 216 can be flushed according to the present invention. A first flush valve 253 and a second flush valve 252 are provided which separate the flush solvent reservoir 228 from the extraction solvent supply, while a high pressure pump 202 is used to add the correct fluids at the correct times during the preparation.

In Figures 7A and 7B, the possible connections of the first flush valve 253 during a flushing step and during an extraction step are shown. During the flushing step shown in Figure 7A, the fluid delivered by the pump 202 is directed to the filter 215 and then into the nozzle 216 to flush it. The other flow path separates the rest of the extraction device from the connection point 213 between the flow paths of the chamber and the bypass leading to the inlet side of the pulsation damper 205. During an extraction step, the position of the first flush valve 253 is preferably changed to that shown in Figure 7B. As shown, the high pressure fluid discharged from the pump 202 is directed directly downstream to the pulsation dampener 205. The other flow path separates the flow between the junction 213 of the chamber and bypass flow path and the filter 215 which is upstream of the nozzle 216.

In the embodiment of Figure 7, therefore, no separate pumping device is needed for the flow of solvent from the solvent reservoir 228. The first purge valve 253 can be inserted anywhere in the flow path, as in the case of the embodiments described above with reference to Figures 4 through 6. In addition to the above-discussed advantages of the device of Figures 5 and 6, the embodiment shown in Figure 7 has the further advantage of using a single pump 202 to deliver both fluids at pressures, flow rates and compositions appropriate to the selected preparation process.

A further aspect of the present invention is that in some embodiments of the methods and devices it is provided that the solution of the extract is diluted with the extraction solvent in order to reduce the concentration of the dissolved components. The solution obtained thereby is more robust against changes in the flow conditions, e.g. passage through lines with different cross-sections, temperature gradients and pressure drops, so that precipitation and/or adsorption of the extracted components along the flow path upstream of the nozzle region is minimized. The dilution is carried out according to the present invention by adding a flow of pure extraction fluid which is fed together with the flow of the extract solution via the bypass section, ie extract plus extraction fluid. In certain embodiments of the present invention, the flow of the pure extraction fluid may be a multi-component solvent mixture. The mixing of the streams occurs before or as the streams flow from the extraction chamber 210 to the nozzle 216, and the fluid streams preferably remain mixed throughout the remainder of the process.

Referring again to Figure 3, it can be seen that the device for reducing the concentration of an extraction solution in a supercritical fluid extraction device preferably includes a valve 207 to allow flow to the bypass section and a valve 209 to allow flow to the region in the extraction chamber 210. A junction point 213 is provided to merge the two flow paths. According to this aspect of the present invention, the device of Figure 3 is not modified except for a change in the degree to which the flow paths are controlled by the device. The correct degree of dilution is obtained by providing a control device for controlling the two valves 207, 209, i.e., for opening, closing and changing the flow rate through the valves 207, 209. As will be readily understood by those of ordinary skill in the art, such a control device may comprise software settings, firmware settings or hard-wired electronic drives. In certain embodiments, a user interface may also be provided to allow the user to select the correct degree of dilution. Finally, the extraction chamber device 210 preferably comprises a computing device for determining the actual chamber volumes flowed through and for communicating the information about the actual extent of contact between the sample and the extraction fluid to the user.

Figure 8 shows an alternative device for reducing the concentration of an extraction solution in an extraction section of a supercritical fluid extractor. As shown, a valve 207 allows flow to the bypass section and another valve 209 allows flow to the area containing the sample. A connection 213 is provided to merge the flow of these two sections. However, in the embodiment of Figure 8, a restrictor 310 is located in the bypass flow path. In addition, in certain embodiments, a further restrictor 320 is located in the extraction chamber flow path. The degree to which the restrictors 210, 230 restrict flow is selected to provide an appropriate ratio of extraction fluid between the two flow paths when both valves 207, 209 of the bypass and extraction sections remain open. The apparatus preferably further includes a controller which, in a "dilution mode", keeps both valves 207, 209 open during the extraction portion of the process of the present invention, or in an "undiluted mode", selectively operates the valves 207, 209, thus enabling timed operation. As described above, the controller may include software controls, firmware controls, or hard-wired electronic drives. As described above with reference to Figure 3, the preferred embodiment of the invention shown in Figure 8 also includes a device for calculating the actual chamber volumes flowing through.

Another embodiment of the device for reducing the concentration of an extraction fluid solution is shown in Figure 9. Again, valves 207, 209 are preferably provided to control the flow to the bypass and extraction sections, respectively, and a connection 213 for merging the flow paths. A mass flow sensor 400 is located immediately upstream of the region 210 containing the sample. As part of the bypass valve 207, a flow control device is provided which adjusts the degree to which the valve 207 throttles the flow located in the bypass section and the flow through the Section 210 containing the sample is changed. Finally, a computing device for calculating and displaying the actual chamber volume flowed through by integrating the instantaneous mass flow rate over time (not shown) is preferably also provided as part of the operation and control system of the extraction device.

Although the methods and devices described above solve a number of problems in certain applications, those of ordinary skill in the art will understand that it is also advantageous to combine the features of the methods and devices described to achieve further improved results. For example, the present invention provides a method for diluting an extract solution in an extraction solvent to reduce the concentration of the dissolved components, thereby providing the advantages explained above, combined with a method for flushing the nozzle throat. Such a combined method according to the present invention comprises selecting the degree of dilution to be used and providing information describing the resulting degree of contact of the sample with the extraction fluid, i.e. the volume flowed through; then the other parameter values to be set are entered or selected. Thereafter, an extraction process is carried out, followed by a flushing process according to the present invention. If necessary, extraction and rinsing steps are repeated sequentially and, in certain embodiments, dilution may also be provided for each subsequent extraction step.

While the samples introduced into the device of the present invention are primarily in the form of solid samples, it is also possible to introduce small amounts (i.e., volumes in the range of microliters or milliliters) of liquid by distributing the liquid on solid supports such as filter paper, adsorbents or powders.

Similarly, semi-solid substances such as fats and creams can also be introduced.

In other embodiments of the present invention, it may be desirable to provide one or more additional nozzle/separator units in addition to the nozzle/separator unit 214 described above with reference to Figure 3. As shown in Figure 10 and discussed above, such additional nozzle/separator units 214 would either be incorporated into the apparatus of the present invention or reside in other devices associated therewith. In some cases, an additional nozzle 216 may be the only additional subassembly. In other embodiments, the nozzle and/or separator units located in other devices may completely replace the subassemblies that are preferably provided as part of the extraction apparatus according to the present invention. In addition, the hardware of the nozzle/separator units 214 can be specifically adapted to perform functions in the apparatus of the invention or the devices in which they are incorporated, such as: injection channels on gas chromatographs, a pre-column or heart cut on liquid chromatographs and supercritical fluid chromatographs. As one of ordinary skill in the art will know, heart cut is a technique used in liquid chromatography to selectively introduce portions of a complex sample introduced into the main column in the liquid chromatograph.

A further modification of the device according to the invention consists in providing a device for connecting additional connections between the remote connection 225 and/or the separator outlets 223, 224 and other analysis devices - e.g. in particular liquid chromatographs, UV/VIS spectrophotometers and liquid samplers - so that the fraction rinsed in the separator 218 can be fed to these devices can be carried out there for further treatment and then analysis.

Similarly, the apparatus disclosed in Figure 3 can be modified to provide for sampling of the fluid solution exiting the extraction chamber 210 prior to recovery of the solutes in the nozzle/separator unit 214 or prior to delivery to other equipment, e.g., through the sections 530 or the fractionation zone 300 shown in Figure 10. For example, the sample stream can be directed, possibly at high pressure, to a UV/VIS spectrophotometer or through sampling valves on a variety of other analytical equipment, such as liquid chromatographs, supercritical fluid chromatographs and gas chromatographs, in a similar manner to that shown in Figure 10, where a fractionation zone 300 has been added. The fractionation zone 300 is a component of the "heart cut" embodiment of the present invention.

As explained above with reference to Figure 3, the separator 218 may be filled with a packing material. However, alternative embodiments of the device according to the present invention may include additional regions containing a chemically active packing material (e.g., conventional liquid chromatographic column packing materials, adsorbents, or other porous material), as well as additional heat zone control and hardware and additional valve equipment to direct the fluid to these regions. The addition of such features allows the device to be used to provide fractionation of the mixture of solution leaving the extraction chamber 210 containing the samples before that solution encounters the nozzle and/or separator unit 214. The flow through the chamber and bypass regions discussed above is coordinated with the operation of the heat zones to deposit sample material in the fractionation zone and then selectively remove components from this zone. The components are removed using one of the device configurations specified above.

In the fields of analytical chromatography and preparative chromatography, it is known to choose stationary phases so that they have a selective interaction with different molecules that come into contact with the stationary phase. If the movement of a mobile phase can move molecules relative to the stationary phase, the selective interaction can lead to a separation of the different compounds. Common mobile phases are liquids, gases and supercritical fluids. Stationary phases can be supported as films or layers on a surface (e.g. in thin layer chromatography, open tube or capillary column chromatography) or on particles with which the fluids can come into contact. Thus, even the surfaces can be considered as the stationary phase, possibly after modification in terms of chemical activity, functionality or size selectivity, e.g. in the bound phase, adsorption chemistry or chirality interaction. It is also known to exploit the physical dimensions of the stationary phase to maximize the selectivity, e.g. in terms of the chosen properties of the mobile phase (van Deemter and Golay equations), or in terms of the diffusion time through the liquid layers and in the pores, or in terms of the spatial geometry (overall size and shape) of the migrating compounds. The last example has more relevance for particles forming the stationary phase. In some cases, the selectivity can be extreme, with some or all of the species migrating with much of the mobile or carrier phase being essentially irreversibly removed from the mobile phase and retained by the stationary phases.

In the context of the present invention, all of the physical or chemical properties that are up to a contribute to some degree to the selectivity of movement among the different migratory species exposed to this stationary phase are defined as "chemically active".

In other embodiments of the present invention, the queue of sampling containers 236 described above may be supplemented by additional fraction queues that may be dedicated to any of the following functions: collecting more automated sampling vials, reading and/or writing labels on the sampling vials (bar labels), further fractionating the components in the fraction solution by stationary phase extraction or other common wet chemical treatments and reactions performed in analytical laboratories to obtain solutions suitable for the chosen analytical procedure, including quantification.

An automated device may be used to place the extraction containers into the extraction chamber 210, to remove the extraction containers from the chamber 210, and to exchange the extraction containers in a waiting/storage area. Reading and writing of the labels on the extraction containers may also be provided in such embodiments.

In certain embodiments, the pump 202 may be modified to provide a pump capable of isocratic, binary or ternary solvent delivery to the extraction device to blend fluids and fluid mixtures, particularly those that are normally liquid at ambient conditions. The base extraction fluid is supplied via suitable tubing or valves, and coordinated control is provided via a workstation or other computerized control device, with commands issued to the solvent valves and the pump. In certain embodiments, therefore, the additional pump channels for mixing the fluids and fluid mixtures (particularly those that are normally liquid at ambient conditions) with the base extraction fluid to produce multi-component extraction solvents can be obtained by incorporating further pumps and valve means into the extraction device to obtain a mixture of the extraction fluid.

Preferably, the valves are designed to select the flush solvent flow and supply the flush solvent pump 230. As described above, the flush solvent pump 230 can withstand system pressure and has a variable delivery rate appropriate to the motions in the liquid chromatography zone. The valve means can direct the fluid to deliver user-selected collection volumes to selected destinations.

Finally, as will be understood by those of ordinary skill in the art of designing such systems, the device of the present invention may be coupled with other devices and techniques in a manner referred to above as "hyphenation technology." Examples of hyphenation technology contemplated by the present invention and discussed above are: high pressure solid phase extraction coupled with supercritical fluid extraction of the samples; solid phase extraction as a precursor to supercritical fluid extraction; low pressure fractionation, in some embodiments refined as solid phase extraction, in the separator 218 to collect the extract, after supercritical fluid extraction of the sample; medium to high pressure fractionation with gases, liquids or supercritical fluids, in some embodiments refined as solid phase extraction, in the separator 218 to collect the extract, after supercritical fluid extraction of the sample, with the effluent directed to analyzers; thermal desorption of the separator 218 for collecting the extract after supercritical fluid extraction of the sample, with the effluent being directed through additional valves to analyzers; flush solvent (i.e., for the reconstituting solvent) connection point to other devices; sampling in the high pressure stream between the chamber 210 containing the sample and the sampling subassembly 214 (the nozzle 216, which also serves as the pressure control mechanism, and the separator 218) so that other devices can monitor or remove the samples from the high pressure stream; high pressure fractionation in a fractionation region located between the chamber 210 containing the samples and the collection subassembly 214; merging the high pressure fractionation with the flow sampling function in analyzers with a flow sampling function to provide a "heart cut" in the analyzers; using subassemblies to collect multiple samples; Using a set of instructions having the following features: (a) providing chaining with other instructions from the user to other destinations so that the sequence of steps of the extraction device can be coordinated with other sequences of steps, and (b) simple instructions from which the sequences of steps could be constructed.

It is contemplated that the present invention may be used in conjunction with other analytical instruments, as shown in the embodiment discussed above with reference to Figure 10, some of which instruments may have a nozzle and/or separator section as described above with respect to the present invention. Such analytical instruments include gas chromatographs, liquid chromatographs, and supercritical fluid chromatographs. In addition, the present invention may also include a fractionation zone 300 for fractionating the extract from the sample. Such a fractionation zone 300 would include valves and a thermal control device connected to the extraction chamber section 210 and the nozzle 210.

The design of the device of the invention applies the knowledge of important parameters and constraints in various areas: supercritical fluids, (supersonic) expansion of fluids, collection/recovery of extract, pumping of compressible fluids, set point control. As explained above, the system uses a fluid compressibility algorithm for pumping the solvent, and it uses a pressure-volume-temperature algorithm so that density can be entered as the relevant parameter for solvency (as opposed to pressure) while providing decoupled control of flow and pressure/density. The system preferably allows flow in a bypass and/or dilution mode. In certain embodiments, the selection of the composition of the extraction solvent fluid is determined by multiple inputs; in other embodiments, the composition of the extraction fluid is selected by providing additional pump channels. In the embodiment described above, which includes suitable valve and control software, both static extraction and dynamic flow extraction can be performed. The concept of the present invention also provides for the control of temperature/pressure in several zones according to specifications based on the understanding of the influence of these parameters on density control, particularly for the critical, near-critical and supercritical regions.

The present invention also provides a method for integrating a density/pressure/temperature algorithm into a user interface for entering setpoints and subsequent control of the parameters. This aspect of the present invention allows the operator to enter density as a parameter to the instrumentation, which uses conventional pressure transducers as part of the electronic control loop to maintain pressure (and hence density) at a user-specified temperature. As explained above, density transducers are not currently suitable for general instrumentation for an electronic control loop to directly control density, but they could be provided in accordance with the present invention.

The present invention also provides a method of operating a supercritical fluid extraction system having an electronic pressure control system and a temperature control system in which a user can enter a desired density to maintain the set density without having to control the flow rate of the extraction fluid to achieve the density set point. First, the operating density and temperatures of the various zones are entered via the user interface. The set density is rounded to a value that is useful as a set point given the control capabilities of the temperature and pressure control loops in the given region of the equation of state. The system then calculates the appropriate operating pressure and notifies the user if the combination of the density and temperature set points results in pressures that are outside the operating range of the device. The system then displays the appropriate operating pressure to the user so that all parameters are visible. Finally, the pressure and temperature setpoints are transmitted to the appropriate control loops to maintain density during extraction or other cycles.

The disclosed methods also provide a means for the operator to focus on the more important parameter of density when selecting the parameter set points for the operation of a supercritical fluid extractor. The operator therefore does not have to use look-up tables which require interpolation between entries for those densities which are at temperatures and pressures which are not shown in the table. During operation, the system gives immediate feedback to the user when a certain density cannot be achieved because operating limits of the interactive parameters are exceeded - eg when a combination of a high density and a high temperature exceeds the possible discharge pressure.

The present invention therefore prevents the user from entering a parameter (pressure) whose non-linear relationship to solvency is not intuitive and changes significantly depending on the isotherm chosen, when solvency is the key parameter in the instrument. Instead, the importance of density as a parameter and the discipline of using it are made clear to new users.

Given the equation of state of a given substance, a control program is created to input the density and then calculate the corresponding pressure at a given temperature. Such a program is a more automated process than a lookup table, as well as a tool for exploring design limits and specifications (temperature and pressure variations that affect the resulting density).

Not only does the present invention encourage the use of density as a parameter more directly proportional to solvency, but it also indirectly instructs the user to use more conservative pressure setpoints, thus leading to longer equipment life. This last point arises from the "S" shape of the isotherm, where at higher densities there is a very large increase in pressure with a very small corresponding increase in density.

Although specific embodiments of the present invention have been described in detail, the present invention is not limited to the embodiments disclosed. Reference should therefore be made to the following claims to determine the scope of the present invention.

Claims (4)

1. Apparatus for supercritical or near-critical fluid extraction of components from a sample, comprising: a pump (102) for pumping a supercritical fluid, which pump has a pump motor and a pump motor speed controller (103); Means for regulating the pressure at the outlet of the pump to a desired pressure (110); a flow system for connecting a flow of the supercritical fluid from the pump (102) to an extraction section (210) for retaining a sample; a variable and controllable expansion nozzle device (108, 216) connected to the extraction section and having a mouth hole with a predetermined opening size ; a trap assembly (218) which is directly connected to the expansion nozzle device (108, 216), the pressure drop across the nozzle device (108, 216) allowing the recovery of dissolved material which has precipitated from the expanding fluid, characterized in that the nozzle device (108, 216) comprises a plurality of expansion nozzles (114), each of the nozzles having a different degree of restriction, and in that the expansion nozzles (114) are formed by an arrangement of static flow restrictors which have different mouth openings and which are arranged between two multi-channel valves (115, 116; 117, 118). 2. Apparatus according to claim 1, comprising means for taking samples of the fluid solution leaving the extraction chamber (210) prior to intercepting the solution products in the nozzle (216) and trap (218). 3. Apparatus according to claim 2 or 3, comprising a fractionation bed means (300) for retaining chemically active packing material to provide fractionation of the mixture of solution leaving the extraction chamber (210). 4. Device according to one of claims 1 to 3, with an analytical instrument (500, 510) which is connected to the fluid stream leaving the extraction section (210) prior to expansion in the nozzle device (108, 216).